Process and arrangement for separating oil from oil containing materials

ABSTRACT

A method for separating oil, water and other components that can be evaporated from an oil-containing material by evaporation. The evaporation is achieved at a lower temperature than the atmospheric boiling point of the component, due to the utilisation of the gas phase established by evaporation of a second component. Means for drying of fluid-containing material comprising a processing chamber and a rotor mounted in said processing chamber is also included. The rotor comprises a number of fixed rotor arms that cannot swing and the inner surface of the processing chamber is smooth.

[0001] The present invention relates to a process for separation of oilfrom oil-containing materials, and means for the same.

[0002] Thus, the present invention relates to drying of different typesof oil-containing sludge. The material on which tests have been carriedout is cuttings and therefore the description given below will focus onthis material. However, it must be pointed out that the invention is notlimited to drying of cuttings.

[0003] In connection with oil exploration, large amounts of oil-baseddrilling sludge are used. Use of oil-based drilling sludge, as opposedto water-based drilling sludge, leads to considerable technicaladvantages in test drilling as well as production drilling of oil wellsboth from land and off-shore based drilling operations.

[0004] Typically, the cuttings consist of granulated stone and claywhich have been brought up from the ground with the aid of drillingfluids (mud) and remains of drilling fluids which the mechanicalseparation methods that are used in connection with the drillingoperations do not manage to remove. Drilling sludge consists of specialbase oils, water, various chemicals and special types of finely groundclay. Very large amounts of this type of waste are generated every yearall over the world, leading to considerable costs for the oil companiesin connection with its handling, transportation and cleaning. Thecleaning implies the removal of oil from the solid matter so that theoil can be re-used for the drilling operations and the solid matter canbe deposited as inert waste or be used as a filling material or suchlike.

[0005] Because of the oil content in the cuttings that come back fromthe drilling well, the cuttings cannot be deposited freely in nature,and the oil must thus be removed from the cuttings to ensure anenvironmentally friendly depositing.

[0006] In particular, it is the fraction of the drilling sludge thatcontains fine grains which causes the problems. The fraction containingcoarse grains is sieved out on vibrating sieves and can be washed beforeit is dumped, or the oil remains can be evaporated off.

[0007] The finely grained fraction that comes from the vibrating sievesor the washing process is normally treated in centrifuges orhydro-cyclones, in which one obtains that a portion of the oil and waterare separated from the sludge.

[0008] The remaining part of the oil is strongly bound to the sludge,and there are no sufficiently satisfactory methods present to separatethis oil from the remaining sludge.

[0009] Conventional processing facilities for this type of waste arebased on indirect heating. This means that the cuttings are in contactwith heating surfaces that are heated by means of, for example, hot oilor flue gas. Several processes based on indirect heating are usedextensively in exclusively land-based installations.

[0010] Among hot oil devices one can mention “CLTU” which is supplied bySoil Recovery Ltd in Denmark and “Thermal-D™” which is marketed byOiltools International. The CLTU process is a so-called dish-drier inwhich the material is heated up by a rotor comprising dishes filled withhot oil.

[0011] The Thermal-D™ devices are so-called “paddle-driers” in which therotor comprises special agitator bodies filled with hot oil. In boththese devices the rotor has the additional function of providing slowtransport of the material through the machine.

[0012] During its passage through the process, the material will begradually heated up so that, because of the different boiling points,water which the material may contain will evaporate first and thereafterthe different oil fractions. Typical boiling point distribution forcommon base oils which are used in drilling fluids lies in the rangefrom 180-200° C. to 280-340° C. Because of the limited applicationtemperature for conventional hot oils, the maximum temperature that thematerial can be exposed to in these processes will lie at around280-300° C., and leads in many cases to insufficient evaporation of theoil in the material, if necessary the processing capacity may be reducedby using a longer residence time for the material so that one achievesapproximately the same temperatures in the material as in the hot oil.

[0013] Processes heated with flue gas often comprise large rotatingdrums through which the material is slowly transported andsimultaneously heated by hot flue gas from the combustion of oil or gasat the outside of the drum. The devices can have different agitationarrangements on the inside to improve the mixing of the material. Thesedevices do not have the same temperature limitations as the hot oilheated processes, as the flue gas can be 800-900° C. However, thistechnology results in very large installations and long residence timesfor the material can lead to thermal degradation of the oil which onewants to recover at the same quality as the original. Among commerciallyused devices, can be mentioned THOR™, which is marketed by VARCOInternational and the ITD process from OnSite™ Technology.

[0014] Furthermore, known within the prior art, is means which uses thefriction principle to generate sufficient energy for the oil fractionsto be evaporated off. This principle is described in the applicant's ownpatent NO 155832. In this process a hammer mill with swinging rotorarms, as well as fins in the stator, are used to finely crush allparticles in the material which one wishes to evaporate. This results inthe heat which is generated ensuring evaporation of the oil in thematerial at a lower temperature than at normal evaporation. With thisprocess one breaks down the capillary forces between the oil componentand solid particles. The fine crushing of the material releases energy,and one will not need to supply the excess heat which normally isrequired to force out the liquid which is bound in capillaries.

[0015] However, this process has limitations and with the presentinvention one aims to provide a process which is a considerableimprovement.

[0016] The extensive crushing of the sludge material is one of thedisadvantages one experiences with the process described in NO 155.832.This fine crushing of the sludge material leads to a large part of theparticles becoming so small that they cannot be effectively retained inthe processing chamber, but are dragged out with the fluid vapour.Furthermore, the particles become so small that it is difficult, nearlyimpossible to separate them out with the methods for gas phaseseparation that can be used with high temperature oil vapour. Theparticles will thereby be transferred to the condensation facility forthis process and end up in the condensed liquid phases. This reduces theutilitarian value of the process considerably because the aim is toreclaim the phases as purely as possible.

[0017] Another limitation with the process described in NO 155.832 isthe construction with fins in the stator. This leads to much wear andtear both on the rotor arms and the fins, and even with the bestavailable materials for hard covering we have experienced that themaintenance intervals become too short.

[0018] The present invention is essentially much different from themethod described in NO 155.832 in that one is not dependent on breakingdown the capillary forces, and that one thus can avoid the unnecessarycrushing of the material. This is achieved by the stator having a smoothinner wall, and by having the rotor arms permanently fixed to limit anyswing movements that can promote crushing.

[0019] It is thus surprisingly found that with these changes one willstill be able to evaporate oils considerably below their normalatmospheric boiling points. Without being tied to a definite theory, itis assumed that the mechanism which can explain the process according tothe invention is an effective so-called “steam stripping”. With this ismeant evaporation of a first component at a temperature substantiallybelow the normal atmospheric boiling point in that the partial pressurein the gas phase of the first component is reduced by adding acomponent, or by an already present second component. The firstcomponent is typically one or several various oils, but the secondcomponent is typically water vapour.

[0020] For example, if one has a first component with a boiling point of300° C. at normal atmospheric pressure and 250° C. at 0.1 atmospheres,one can by steam stripping evaporate this first component in a containerat atmospheric pressure and 250° C. To do this, the container must besupplied with an amount of water vapour (the second component) whichtakes up 90% of the volume of vapour that comes out of the container.Thereby the gas volume of this component will be 10% and thecorresponding partial pressure 0.1 atmospheres.

[0021] To get the full effect of steam striping it is necessary for thefirst and the second component to be so different that one does not getany molecular interaction between the two components. In separation ofoil from oil-containing sludge and by application of water as the secondcomponent these conditions are met.

[0022] At separation of a first component from a sludge material, onecan also in principle add a second component so that the steam strippingconditions are met, to get the first component evaporated at atemperature considerably below the atmospheric boiling point of thecomponent.

[0023] As mentioned above, the process according to the invention istested on different oil-containing cuttings, and this material containssufficient amounts of water for it not to be necessary to add more waterfor the principle to function.

[0024] A presently preferred embodiment of the present inventionutilises the water which is already present together with the oil in thecuttings to provide a stream stripping effect.

[0025] Drilling waste does rarely have a water/oil ratio which is lessthan 1:2 based on mass. Typical base oils which are used in drillingfluids encompass paraffin oils with a carbon chain length of minimum C₁₁to maximum C₂₃ with an average of C₁₆. Thus, the average molecularweight of the oil is 216 g/mol, in contrast to 18 g/mol for the water.With a mass ratio of 1:2 the volume fraction of oil vapour when allwater and oil have evaporated will then be=({fraction(2/216)})/({fraction (1/18)}+{fraction (2/216)})=14%. This means that ata working pressure of, for example, 1.2 atmospheres, the average partialpressure of oil vapour in the processing chamber will be 0.17atmospheres. At such pressure one will have a boiling point reductionfor the oil of around 50° C., which implies a considerable reduction inthe necessary processing temperature to achieve complete evaporation ofoil from the material. Most base oils used in drilling fluids will becompletely evaporated at around 300° C., which is in a range whereunwanted thermal degradation processes do not dominate, and in a rangein which it is reasonably straightforward to design systems whichsatisfy the specific safety demands for operation of offshoreinstallations.

[0026] Thus, with the process according to the present invention, oneobtains that the evaporation will take place nearly instantaneously inan approximately homogenously mixed container with very strongagitation.

[0027] This leads to a substantial improvement of the existingtechnology for drying of oil-containing sludge materials. Although theprocess described in NO 155.832 is the technology which is technicallyclosest to the process according to the invention, this has as mentionedlimitations with respect to finely crushed particles that it has notfound widespread application. When considering the advantages which areobtained with the present invention, the invention must be compared withthe indirect driers which are presently used for separation of suchoil-containing sludge material.

[0028] In contrast to the slowly rotating indirectly heated processes,the process according to the present invention, because of thefrictional heat that is generated and because of the material not beingfinely crushed, makes it possible to utilise steam stripping by usingthe water that is present in the material.

[0029] If one considers a slowly rotating indirect process, differentdefined phases will dominate at different places along the longitudinalaxis of the process:

[0030] 1. Preheating phase: The first part of the process where all theheat which is supplied is used to raise the temperature of the material.

[0031] 2. Water evaporation phase: When the material is heated to theboiling point of water, most of the supplied energy will be used toevaporate free water.

[0032] 3. New preheating phase: When the free water has disappeared, thesupplied energy is used to increase the temperature to the boiling pointof the lightest oil components and bound water.

[0033] 4. Oil evaporation phase: As gradually heavier oil fractions areevaporated the temperature will progressively rise. Maximum temperatureat the end of the process is decisive for how much oil is left in thematerial. For steam liberated in phase 2 to be available for steamstripping of oil in phase 4, the steam must effectively be brought intocontact with the material that is in phase 4. In the solutions that areknown within the prior art, it is difficult to promote such contact. Toa large extent the steam will pass over the material on its way to theexit for exhaust vapour without an effective mixing between steam andmaterial.

[0034] The present invention also provides a means that is designed foreffectively carrying out the process according to the invention. Thismeans will now be described in more detail with reference to theenclosed figures, in which:

[0035]FIG. 1 shows a principle drawing of a drying means according tothe invention.

[0036]FIG. 2 shows as section and segment an embodiment of a meansaccording to the invention.

[0037] The process according to the present invention is thuscharacterised in that evaporation of a fist component occurs at a lowertemperature than the atmospheric boiling point of the first component byutilisation of the gas phase which is established by evaporation of asecond component, as the second component has a molecular weight whichis larger than the molecular weight of the first component, and that thesimultaneous presence of the vapour phase of the second componentconsiderably reduces the partial pressure of the first component in thegas phase that surrounds the material.

[0038] Further alternative embodiments are described in the subclaims2-7. presently preferred embodiment of the invention comprisesseparation of water and oil from cuttings, i.e. the first component isoil and the second component is water.

[0039] The present invention also relates to an improved friction dryercomprising a processing chamber with at least one inlet opening, andwith a rotor mounted in this processing chamber, with an annular spacefor taking up of the material which is to be dried being establishedbetween the inner surfaces of the processing chamber and the outersurfaces of the rotor, characterised in that the rotor comprises anumber of fixed rotor arms that cannot swing which end at a distanceinside the inner surface of the processing chamber, and that the innersurface of the rotor is smooth.

[0040] Further embodiments of the means are described in the subclaims9-20.

[0041] Thus, the present invention also relates to a drying means (10).In practice, the means (10) is shaped as a cylindrical processingchamber (12) (stator) with an internally mounted rotor (14). The rotor(14) is equipped with a number of rotor arms (16) which end a shortdistance inside the static cylindrical container (12).

[0042] In the most common types of materials which one wishes to dry,and with rotor arms (16) made from conventional steel alloys, one cangive the following characteristics for construction of the drying means(10):

[0043] 1. Diameter of cylindrical processing chamber: 0.5-5 m, typicallyaround 1 m.

[0044] 2. Tangential velocity of the tip of the rotor arms: 10-100 m/s,typically around 35 m/s.

[0045] 3. Radial clearance between the wall of the processing chamberand rotor: 0-0.1 m, typically about 0.03 m.

[0046] 4. Number of rotor arms (16) in relation to area of thecylindrical inner wall of the processing chamber (12): 10-100 per m²,typically about 30 per m².

[0047] 5. Total projected front area (16 a) for the part of the rotorarms that is in ingress with the bed of material viewed in the directionof movement in relation to the total volume of the bed of material:0.1-1 m²/m³, typically about 0.5 m²/m³.

[0048] The length of the processing chamber (12) and the dimensions ofthe rotor arms (16) in tangential direction is of less importance forthe processing. The directions for these will be given by the mechanicalstrains the construction must withstand, and the demands for effectiveremoval of the steam that is generated in the material bed. Byincreasing the tangential velocity, one gets considerable possibilitiesfor varying the different parameters defined above.

[0049] The essential of the drying means (10) is that this is formed sothat the three basic physical processes of mixing, generation of heatand evaporation are in correct relation to each other. To obtainsufficient generation of heat by means of forces of internal collisions,contacting and friction, it is necessary to have high tangentialvelocities of the rotor arms (16) as indicated in item 2 above. Thenumber of rotor arms (16) must not be too high, and the arms (16) mustnot be placed too close as this can lead to the material in the bed to alarge extent rotating together with the rotor, more or less like a solidbody. The forces of friction will then mainly arise between the bed ofmaterial and the wall of the cylindrical container (12). This willresult in too low heat generation to obtain effective evaporation.Furthermore, the mixing process will be ineffective, and it will beimpossible to maintain a stable and dry bed of material. The otherextreme, namely the distance between the rotor arms (16) being toolarge, is not good either. Then, not enough of the bed material willparticipate in the energy transfer mechanism that is described above,which will lead to both ineffective mixing and too little evaporation.The result is that local zones with too high moisture content willarise.

[0050] Good results are obtained with the combination of parameters asare given in items 3-5, and a presently preferred embodiment of theinvention is means (10) with the following characteristics:

[0051] 1. Diameter of cylindrical processing chamber is around 1 m.

[0052] 2. Tangential velocity of the end of the rotor arms lies in therange 30-40 m/s, preferably around 35 m/s.

[0053] 3. Radial clearance between wall (12 a) of the processing chamber(12) and the front area (16 a) of the rotor arm (16) is about 0.03 m.

[0054] 4. Number of rotor arms (16) in relation to the area of the innerwall of the cylindrical processing chamber is 30 per m².

[0055] 5. Total projected front area (16 a) for the part of the rotorarms which is in ingress with the bed of material viewed in thedirection of movement in relation to the total volume of the bed ofmaterial is about 0.5 m²/m³.

[0056] A sufficiently rapid mixing is important. With the typicalcombination of tangential velocity, clearance and diameter as indicatedin items 1-3 above, the individual particles in the bed of material willbe able to move round the whole circumference of the bed of materialabout 12 times per second. This will give a mixing in the tangentialdirection which is very rapid and effective. One will not find gradientsin the oil content in a tangential direction in such a device, apartfrom in the area immediately downstream from the feeding points. In anaxial direction on the other hand, the mixing time will be somewhatlonger, as the mixing mechanism is more indirect than in the tangentialdirection. This can mean that one can find gradients in the oil contentin the axial direction with maximum values in the axial positions wherefeeding takes place. To succeed with the processing it is essential thatfeeding is regulated so that the average oil content around the wholecircumference at the feeding points are adjusted so that the demands forremaining oil content in the dry material is met. A smootherdistribution of feeding point in an axial direction will render theprocess less dependent of an effective axial mixing, and an embodimentaccording to the invention thus relates to a means (10) where severalfeeding points are arranged along the axial direction of the means (10).

[0057] To create the necessary heat generation, the demand for effectivemixing must be met at the same time. The rotor arms (16) will mainlyensure that the particles in the bed material are thrown in a tangentialdirection, but movements of less systematic nature are also generated inan axial direction, ensuring axial mixing in the bed of material. Thishelps to collect the bed of material along the inner wall of thecylindrical container (12) with forces which greatly exceed the tendencyof the force of gravity to collect material in the bottom of thecontainer (12). The pulling forces from the vapour that is generated inthe bed of material are not strong enough to transport substantialamounts of material towards the centre of the container either.Therefore, the exhaust vapour is led out from the processing/dryingchamber itself via an exit (20) situated as centrally as possible. Thiscontributes to reducing the pulling along of particles in the exhaustvapour to an acceptable level.

[0058] If one compares the means according to the invention to thesolution that is closest technically, i.e. the means which is describedin NO 155.832, then the main differences are that the means according tothe present invention firstly is not equipped with longitudinal wearingfins, and secondly, there is no impact arms mounted on the rotor plates.

[0059] Furthermore, the embodiment which is outlined in NO 155.832 hasan inlet opening for material in the one end-wall and exit for drymaterial in the other. This leads to the contact between steam which isformed in the first part of the process and particles in phase 4 in thelast part of the process being much poorer than in a homogeneously mixedcontainer, because there will be an even flow of oil vapour frommaterial in phase 4 towards the gas volume within the bed of materialwhich prevents steam from coming in contact with, and be mixed with, theparticles.

[0060] With the means according to the present invention the individualparticles that are fed in will very quickly be spread over the whole ofthe bed of material in the processing chamber due to the positioning ofthe feeding opening(s) and the construction of the apparatus. Eachindividual particle will go through the four phases indicated above, butthe intensive mixing will ensure that there will be particles in all thefour phases throughout the whole of the bed of material all the time. Ifone considers a given number of particles, the gas that surrounds theparticles in the bed will have the same mixing ratio between watervapour and oil vapour throughout, and this must be given by the amountof water and oil in the material. Around every particle in a fluidisedbed there will be a laminar boundary layer of a given thickness.Molecules that are evaporated from the surface of the particle mustdiffuse through this boundary layer to get to the turbulenthomogeneously mixed gas phase outside, and the thickness of the boundarylayer is decisive for the concentration gradient which sets the rate ofdiffusion and thereby the rate of evaporation. As long as the partialpressure of the oil in the homogeneous bulk gas phase is below thevapour pressure at the prevailing temperature, the oil molecules willdiffuse through the laminar boundary layer and into the gas phase. Thethinner the boundary layer, the more effective the stream stripping ofoil from a particle that is in phase 4 will be. The high rotationalspeed which is necessary to keep the material in the processing chamberhomogeneously mixed gives at the same time also a much effectivereduction in the thickness of the laminar boundary layer.

1. Process for separation of oil, water and other components that can beevaporated from an oil-containing material such as cuttings, bleachingearth, sludge waste from oil tanks, oil shale and the like byevaporation in a neutral atmosphere, in a rapidly rotating frictiondryer with fixed rotor arms (16) and a smooth inner surface,characterised in that the evaporation of a first component occurs at alower temperature than the atmospheric boiling point of the firstcomponent by utilisation of the gas phase that is established byevaporation of a second component, with the second component having aboiling point which is below that of the first component, and that thesimultaneous presence of the vapour phase of the second componentsubstantially reduces the partial pressure of the first component in thegas phase surrounding the material.
 2. Process in accordance with claim1, characterized in that the rotation in the friction dryer issufficient to reduce the thickness of the laminar boundary layer thatsurrounds the particles so that the concentration gradient for vapour ofthe first component from the surface of the particles and into the gasmixture which does not have a high content of vapour from the firstcomponent is as steep as possible.
 3. Process in accordance with one ofthe claims 1-2, characterised in that the first component is oil, oroil-like compounds.
 4. Process in accordance with one of the claims 1-2,characterised in that the second component is water.
 5. Process inaccordance with claim 4, characterised in that the second component isadded to the material from which oil is to be separated.
 6. Process inaccordance with claim 4, characterised in that the water which is usedas the second component is present in the material before the separationprocess starts.
 7. Process in accordance with one of the claims 1-6,characterised in that the friction dryer has a speed of rotation in therange 10-100 m/s.
 8. Rapidly rotating friction dryer (10) for drying offluid-containing material comprising a processing chamber (12) with atleast one inlet opening (18), and a rotor (14) mounted in saidprocessing chamber (12), with an annular space for taking up of materialwhich is to be dried being established between the inner surfaces (12 a)of the processing chamber (12) and the outer surfaces of the rotor (14),characterised in that the rotor (14) comprises a number of fixed rotorarms. (16) that cannot swing, which end at a distance within the innersurface (12 a) of the processing chamber (12), and that the innersurface of the stator is smooth, and that the rotor (14) is rotated sothat a tangential velocity of the tip of the rotor arms (16) isestablished in the range 10-100 m/s.
 9. Rapidly rotating friction dryer.(10) in accordance with claim 8, characterised in that the tangentialvelocity of the tip of the rotor arms (16) is in the range 30-40 m/s,preferably about 35 m/s.
 10. Rapidly rotating friction dryer (10) inaccordance with claim 8, characterised in that the rotor arms (16) arearranged at a mutual distance apart so that mixing of the material beingfed in and the material in the bed is sufficiently rapid so that nosystematic gradients of the oil content in the tangential direction ofthe means (10) can be demonstrated.
 11. Rapidly rotating friction dryer(10) in accordance with claim 8, characterised in that the radialclearance between the inner surface (12 a) of the processing chamber(12) and the end edge (16 a) of the rotor (16) is of the order 0-0.1 m,preferably about 0.03 m.
 12. Rapidly rotating friction dryer inaccordance with claim 8, characterised in that the number of rotor arms(16) in relation to the area of the cylindrical inner surface (12 a) ofthe processing chamber (12) is of the order 10-100 per m².
 13. Rapidlyrotating friction dryer (10) in accordance with claim 8, characterisedin that the number of rotor arm (16) in relation to the area of thecylindrical inner surface (12 a) of the processing chamber (12) is about30 per m².
 14. Rapidly rotating friction dryer (10) in accordance withclaim 8, characterised in that the total area of the active frontsurface (16 a) of the rotor is of the order 0.1-1 m²/m³.
 15. Rapidlyrotating friction dryer (10) in accordance with claim 8, characterisedin that the total area of the active front surface (16 a) of the rotoris about 0.5 m²/m³.
 16. Rapidly rotating friction dryer (10) inaccordance with one of the claims 8-16, characterised in that the means(10) comprises a number of inlets (18) distributed along the axialdirection of the means (10).
 17. Rapidly rotating friction dryer (10) inaccordance with one of the claims 8-16, characterised in that moisturecontent and forces of collision, contact and friction are indicated bysensor(s) in the processing chamber (12), and that the signal is sentfrom here to a control unit which adjusts the rates of feeding andoutflow, m_(i) and m_(o) respectively, so that a process in accordancewith one of the claims 1-7 is obtained.
 18. Rapidly rotating frictiondryer (10) in accordance with one of the claims 8-18, characterised inthat the stator and/or rotor are fitted with heating surfaces. 19.Rapidly rotating friction dryer (10) in accordance with claim 8,characterised in that the volume of the processing chamber in whichtransfer of heat and evaporation takes place can be limited to 1.0 m³per tonne treated cuttings per cycle.